1. Field of the Invention
The present invention relates, in general, to a shift control method in a dual clutch transmission (DCT) (hereinafter referred to as the “DCT vehicle”) and, more particularly, to a shift control technology for a vehicle that is traversing on rough terrain during power-off downshifting.
2. Description of Related Art
A DCT is a transmission that uses two clutches as well as a transmission mechanism of a conventional manual transmission, in which actual gear shifting is carried out through conversion of the engagement status of two clutches in the state in which shifting gears of a target shift stage are previously fastened.
With an automatic transmission having a conventional torque converter, it is relatively easy to achieve a smooth and comfortable feeling of shifting since the torque converter absorbs shock that occurs during shifting through fluid slip. In contrast, a DCT does not have a device which absorbs shock that occurs during shifting since it does not have a torque converter. In the DCT, the two clutches must be very precisely controlled during shifting in order to achieve a smooth and comfortable feeling of shifting. When the two clutches are implemented as dry clutches, more precise control is required.
During power-off downshifting, an input shaft speed change rate, which is a differential component of an input shaft speed, is used for the purpose of shift control. The input shaft speed change rate is influenced by the conditions of the road on which the vehicle is traversing. Although typical flat road conditions are not a serious problem, a concave-convex road or rough terrain makes the shift control difficult since it is difficult to obtain reliable values from the concave-convex or rough terrain.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.